1. History of the Invention
The present invention relates to a method and apparatus for printing human-readable and machine-readable indicia on printable media, and more particularly to a method and apparatus for printing human-readable characters and machine-readable representations thereof on the same page.
2. History of the Prior Art
With the continued development of data processing equipment and the capabilities and applications therefor, it has become necessary or desirable to be able to machine-read printed characters in various applications. Such requirement may arise, for example, where typewritten characters on a page are to be stored, communicated or otherwise processed. One common way is to scan the page by an appropriate scanning matrix device and store it as non-coded information. Each character space is constituted of cells or pels. As each character is scanned using an array of photodiodes the various pels of the character cell are binary encoded in accordance with the presence or absence of indicia thereat. Typical character cell dimensions are 24 by 40 pels. This dictates a storage requirement of 960 bits for each character. This translates into a storage capacity requirement of approximately 500 kilobits for a complete page of data, assuming the use of a conventional compression technique.
It will readily be appreciated by those skilled in the art that storage requirements of up to 500 kilobits per page can be highly disadvantageous from the standpoint of space, expense and other factors. One method of reducing this requirement is by optical character recognition. There are several disadvantages and limitations upon the use of conventional OCR techniques with human-readable characters. For one thing most such systems are limited to use with a single character font. In such situations it may be difficult or impossible to use or recognize other types of font such as italicized characters, underlined characters and the like. Further problems in the nature of registration, skewing, segmentation and the like arise as the result of the difficulty in having to scan and store information for the large number of pels defining each individual character. In such situations large arrays of photodiodes or like elements must be accurately positioned if the binary information corresponding to the characters is to be generated accurately. Further problems may arise as a result of the inability to store and communicate representations of typewriter functions such as "tab" in addition to the characters themselves.
Even in instances where the characters to be optically scanned are limited to a single font system, recognition problems may arise due to other factors such as in the case of proportional typing where character width may vary on a character-by-character basis. Moreover, certain font systems and certain types of characters have proven to be incompatible with OCR techniques because of such things as the configuration of the font system or the number of different characters that must be recognized. Thus, in the case of oriental characters where a single alphabet may be comprised of thousands of different characters, OCR techniques may be impractical or impossible because of the extremely large storage capacity required in some cases and the inability to satisfactorily distinguish between and thereby recognize the individual characters in still other cases.
Varieties of equipment have been developed in an effort to provide greater capability in the recognition and processing of different types of printed characters. In U.S. Pat. No. 3,578,136 of Postal, for example, a teletypewriter is modified so as to be able to print different types of characters using coded ink in conjunction with coded photoluminescent components. Examples of systems which provide a machine-reading capability in conjunction with human-readable characters are provided by U.S. Pat. No. 2,958,568 of Hagelbarger, U.S. Pat. No. 3,515,061 of Ritzerfeld, U.S. Pat. No. 3,541,960 of Dilsner, U.S. Pat. No. 3,614,394 of Bindshedler and U.S. Pat. No. 3,719,262 of Taplin. In the Bindshedler patent human-readable characters are also magnetic so as to be machine-readable. In the Hagelbarger patent the various type elements of a typewriter type each human-readable character and at the same time make a magnetic recording thereunder. In the Taplin patent visible and invisible but machine-readable versions of each character are superimposed. In the Ritzerfeld patent coded information is recorded together with the printed matter. In the Dilsner patent a coded character is printed in a space in the middle of conventional uncoded characters.
While the systems described in the above-noted patents solve some of the problems present in the prior art, they still leave much to be desired. For one thing, most such systems require extensive revision to or redesign of conventional printing equipment and the electronics associated therewith. Of at least equal importance is the fact that such systems abandon optical character recognition in favor of magnetic recording and sensing and other techniques which may at the very least be impractical for many applications such as where large volumes of typewritten messages are to be processed.
Accordingly, it would be desirable to provide a method and apparatus capable of printing and recognition of both human-readable and machine-readable characters, which system is of relatively simple design and may require only minor modifications to a standard piece of equipment such as a memory typewriter. It would furthermore be desirable to provide a method and apparatus in which human-readable characters can be made available for optical recognition in relatively simple and straightforward fashion so as to lend itself to use with various different character sets and font systems as well as various spacing or organizational commands.